function nicplot(cx,cy,r,s)
% Plot gain contours for Nichols plot
%kja 071005
fi=-3*pi/2:pi/1000:pi;
z=cx+r*cos(fi)+i*(cy+r*sin(fi));
x=real(log(z));y=unwrap(imag(log(z)));
cp=plot(-y,x,s);
set(cp,'Linewidth',1);